generally structural (ex collagen, keratin, elastin
generally receptors or channels that facilitate or control transport of molecules through membranes
results from association of several "subunit" polypeptide chains, linked by hydrogen or electrostatic bonding to form an oligomer
Conformational change in quarternary structure
conformational change in one subunit may affect structure and function of other subunits (ex hemoglobin)
is the conformation in which a molecule is biologically active
proteins that assist the non-covalent folding or unfolding and the assembly or disassembly of other macromeloecular structures, but do not occur in these structures when the structures are performing their normal biological functions
Folding of proteins
occurs during synthesis, aided by chaperones
Can denatured proteins regain native conformation?
No. Denatured proteins do not spontaneously regain native conformation.
Amino Acid Polarity:
tendency to interact with water; non-polar amino acids are hydrophobic
AA Electrical charge:
based on ionization at physiological pH
have no charge in R group, so amino (+) and carboxy (-) group charges cancel each other and result in no net charge.
AA classification by
-polarity -electric charge -structure (of side chain)
Side chains that are electrically charged or contain hydroxyl groups are __________ and interact with water, so tend to orient ____________ part of the protein.
polar tend to project on the surface of proteins
Side chains with phenyl rings are _________, hydrophobic, and often orient ___________ of protein structures.
nonpolar orient toward the inside of protein structures
Acidic side chains ___________ hydrogens.
Basic side chains __________ hydrogens.
AA can act as a buffering system in blood by
AA in proteins accept hydrogens when pH is too low, and donate hydrogens when the pH is too high.
Aliphatic AA side chains
contain hydrogen or hydrogen and carbon in straight chain or branched configuration (non-cyclic/non-aromatic)
Sulfur containing AA are polar or nonpolar; hydro- phobic or philic?
Post-translationally & biosynthetically formed sulfur containing aa
Essential (indispensable) amino acids:
AA's that cannot by synthesized in the body and must be present in the diet.
Totally indispensable amino acids:
cannot be synthesized sufficiently from their alph-keto acids
What are the totally indispensable aa's?
Threonine, Histidine, Lysine
Conditionally indispensable aa's
physiological circumstances can prevent synthesis of an amino acid from its precursor (ie; compromised liver function, inborn errors of metabolism)
Exogenous protein sources:
ingested dietary protein from animal and plant foods
-desquamated mucosal cells (50g pro/d) -digestive enzymes and glycoproteins (17 g pro/d)
Digestion of protein involves denaturation of ______, ______ & _____ by gastric acid, allowing .....
denaturation of the quanternary, tertiary and secondary structures by gastric acid, allowing enzyme access for hydrolysis of the peptide bonds in the primary structure.
Enzymatic "hydrolysis" of peptide bonds begins with _______ in the ______, and involves the addition of ____ molecule of _____.
pepsin in stomach involves the addition of 1 molecule of water
Enzymes involved in digestion of protein in the stomach: